This invention relates to noise suppressing apparatus for gas turbine engines. More particularly, this invention relates to apparatus for reducing the combustion noise level of gas turbine engines.
The noise generated by a gas turbine engine comprises a number of noise components, each of which is generated by various noise sources within an operating gas turbine. For example, one major component of noise is caused by the rotating turbomachinery included within the compressor assembly, the turbine assembly and the fan assembly of a turbofan engine. A second major component of noise is the jet noise that is generated by the mixing of the turbine exhaust gases with the ambient air, while yet a third component of noise is the combustion noise that results from the burning of fuel within the gas turbine combustor assemblies.
Recent advances in the design of gas turbine engines have not only improved engine performance, but have also greatly reduced the overall engine noise level. Specifically, the development of the high bypass ratio turbofan engine has significantly reduced jet noise by reducing the mean jet velocity. Improved acoustic lining techniques and materials, utilized within the air inlet and passageways of recently designed gas turbine engines, have provided reductions in turbomachinery noise such as fan noise, compressor noise and turbine noise. Even with these advances in engine noise reduction, the noise emitted by gas turbine engines such as those employed on transport aircraft remains higher than desirable, with the result that governmental control is periodically effected to reduce the permissible noise level of new engine designs or even to restrict the use of currently operational engine designs. With the previously mentioned reductions in turbomachinery noise and jet noise, combustion noise, which was once considered to be a relatively minor noise source, has become important to the extent that further reduction of overall engine noise level generally requires a decrease in the generation of combustion noise.
Although the factors that influence the generation of combustion noise have not been totally analyzed and understood, it is known within the art that the frequency spectrum of aircraft engine combustion noise includes frequency components within the range of 100-1,000 Hz, with the frequency spectrum peaking generally between 200 and 600 Hz. Further, it is known that, although the primary source of the combustion noise is the combustion process, the structural configuration of the engine combustors or combustion chambers influences the magnitude of the combustion noise components.
Within the prior art, reductions in combustion noise have generally been effected by parametric tests in which combustor design parameters (e.g., the arrangement and configuration of the openings in the combustor wall that supply pressurized air from the compressor stage to the interior of the combustor) are varied. Other approaches to combustion noise reduction include muffler-like apparatus that is mounted downstream of the engine combustors, acoustic lining materials peripherally mounted around the combustor walls, and treatment of the combustor flame holder.
Although successful to some degree, none of the prior art attempts have proven totally satisfactory. Further, such attempts have often resulted in decreased engine performance and an increase in engine weight, or have resulted in a configuration that can only be employed within a new engine design.
Accordingly, it is an object of this invention to provide apparatus for reducing the level of combustion noise generated by a gas turbine engine.
It is another object of this invention to provide a low noise burner can assembly for use in a variety of gas turbine engines,
It is yet another object of this invention to achieve the above-mentioned objects such that the invention can be utilized in either present engine designs or newly designed engines without a significant increase in engine weight or a significant loss in engine performance.